Like dividing by zero

Are you trying to create a black hole!?

Whoah I need to do that!!!

It would be black. If you made a room with 4 walls, a ceiling and floor, and no possible light source or window to let light in, it would be dark. There'd be no light getting in.

Well actually, if there was some sort of light, it would be green. Mirrors reflect green light. Try putting a mirror up to a mirror

I keep running into walls because it would look big

You would probably see your reflection twice, backwards and frontwards. I really don't know.

http://themetapicture.com/a-box-full-of-mirrors/

But you'd have to have some way to look inside the room, or some source of light, so the light, or door or even the tiniest crack would be reflected. Unless you have two way glass, so it would be hard to see inside.

it would look dark but you could never tell because you couldn't get a person or camera in it without ruining the blank reflection